Over 200,000 new cases of breast cancer are diagnosed every year in the United States, according to the National Cancer Institute. Between 5 and 10 percent of these cases are believed to be due to an inherited predisposition, where a genetic mutation passed in the family is likely the culprit to increase the chances that breast cancer will develop in family members who inherit the mutation.
Inherited Increased Susceptibility
Usually an individual inherits two normal, functional copies of a given gene, one from each parent. Over the course of his lifetime, one copy of the gene could be inactivated by a random mutational event. However, the other healthy copy of the gene would still be able to provide the normal function. If an individual begins by inheriting one mutated copy of the gene, then there would be no backup if the other copy is mutated later in life. This could have important implications if the gene in question provides protection against developing cancer.
BRCA1 and BRCA2
There are two genes thought to be responsible for the majority of inherited breast cancer: BRCA1 and BRCA2, where BRCA stands for BReast CAncer. The inheritance of a non-functional version of one of these genes increases the likelihood that an individual will eventually develop cancer, it does not guarantee that she will always get this disease. When a mutation in one of these genes is known to be present in a family, family members can easily be tested for the same mutation. Some populations are more likely to have specific mutations, which also facilitates testing. For example, those of Ashkenazi Jewish descent are most likely to have inherited one of three precise mutations, and screening tests for these individuals can be specific for those three changes.
Other Involved Genes
In families where a susceptibility to breast cancer appears to be inherited but there are no BRCA1 or BRCA2 mutations, other inherited mutations may be responsible. These mutations may be in other cancer-fighting genes such as cadherin1 (CDH1), phosphatase and tensin homolog (PTEN), serine/threonine kinase 11 (STK11) and tumor protein p53 (TP53), to name a few. The normal function of these genes is to prevent cells from accumulating mutations that would allow them to become cancerous and/or to prevent cancerous cells from becoming mobile and spreading in the body. So they are often called tumor-suppressor genes. When a mutation in a tumor-suppressor is inherited, it increases the likelihood that an individual will ultimately develop cancer.
